S3 suspend is dangerous. You can corrupt drives and lose your whole array messing around with it.
I don't know how I can explain it differently ... S3 is not something that even can be "built-into" unRAID. It depends on way too many other variables, such as your BIOS, your PSU, your chipset, etc.
The only thing unRAID can do, is include the S3 module. If it was not there, you could not do S3. unRAID has the s3 module. That's all that can be done from unRAID's perspective.
Your frustration that you can't wake up your box from S3 is YOUR HARDWARE'S FAULT. Your hardware either has crappy Linux drivers, or implements the standards improperly, or any of 100 different bugs related to ACPI on Linux and S3 suspend mode.
Did you try an Intel NIC, and disable the Realtek on the mobo? That's the first thing I would try.